1. Field of the Invention
The present invention relates to a triple action pressure switch apparatus comprising a first switch means which is set in one of ON and OFF states when a pressure of a pressurized fluid is set to fall within a predetermined range, and is set in the other one of the ON and OFF states when the pressure of the pressurized fluid is decreased below the lower limit of the predetermined range or is increased over the upper limit of the predetermined range, and a second switch means which is set in one of ON and OFF states when the pressure of the pressurized fluid is set to be higher than a predetermined value within the predetermined range, and is set in the other one of the ON and OFF states when the pressure of the pressurized fluid is set to be lower than the predetermined value.
2. Description of the Related Art
The triple action pressure switch apparatus described above is used in, e.g., an automotive air conditioner. The first switch means of the triple action pressure switch apparatus is connected to an electrical circuit for a compressor or an electrical circuit for an alarm of the air conditioner, and the second switch means is connected to an electrical circuit for a fan motor of a condenser of the air conditioner.
When the pressure of a coolant in the automotive air conditioner is increased over the upper limit of an appropriate predetermined range or is decreased below its lower limit, the first switch means turns off the electrical circuit for the compressor or turns on the electrical circuit for the alarm. When the pressure of the coolant is increased over a predetermined value within the predetermined range, the second switch means turns on the electrical circuit for the fan motor of the condenser.
The fan motor for the condenser is important for an air conditioner of a compact front-wheel drive vehicle in which an installation space of the condenser is limited, and when an outlet pressure of the coolant is increased and the temperature upon delivery of the coolant is increased, the heat exchanging power of the condenser tends to be short.
Triple action pressure switch apparatuses as described above have already been known in Japanese Utility Model Disclosure (Kokai) No. 59-82936 and U.S. Pat. No. 4,591,677. Each of the triple action pressure switch apparatuses described in the above utility model and patent employs one compression coil spring and two snap discs. The compression coil spring is employed to turn on/off the first switch means at the lower limit of the predetermined range. One snap disc is used to turn off/on the first switch means at the upper limit of the predetermined range. The remaining snap disc is used to turn on/off the second switch means at the predetermined value within the predetermined range.
In these conventional triple action pressure switch apparatuses using the compression coil spring, when the pressure of the coolant does not reach the lower limit of the predetermined pressure and a vibration acts on these conventional apparatuses, expansion/contraction of the compression coil spring due to the vibration may cause an erroneous operation of these conventional apparatuses at the lower limit of the predetermined range.
The compression coil spring sensitively causes chattering in response to a variation in pressure of the coolant near the lower limit of the predetermined range. Since the chattering exert a bad influence on an electronics apparatus located near the pressure switch, the chattering must be prevented. In particular, an electronics apparatus for controlling the action of an internal combustion engine must be prevented from being exerted a bad influence by the chattering produced at the pressure switch in the automotive air conditioner.
The compression coil spring requires a large actuating space in its axial direction. This space makes the axial size of the conventional triple action pressure switch apparatus relatively large.
It is difficult for the compression coil spring to set a free length or spring coefficient in its manufacturing process with high precision. For this reason, the coil spring requires a screw type biasing-force adjusting means. The screw type biasing-force adjusting means makes the structure of the triple action pressure switch apparatus complicated and bulky. In addition, although an operation for setting a predetermined preload in the compression coil spring is cumbersome, precision that can be possibly achieved by the setting operation is not so high.